Estratégias analíticas para determinação de Cd e Hg empregando espectrometria de fluorescência atômica com geração química de vapor.

Abstract

In this present work, analytical strategies for the determination of Cd and Hg in sea water samples using Atomic Fluorescence Spectrometry with Cold Vapor Generation (CV AFS) were applied. For the development of the method an adaptation in the cold vapor generation system was performed. To reduce the sample/reagent consumption and improving the stability of the analytical signal of the technique. The multivariate optimization methodology was also employed, for both analytes. Beginning with a complete two-level factor design (23), which was used to evaluate the trend of the variables: HCl concentration, NaBH4 concentration and carrier gas flow (CGF). Within the established experimental domain all factors were statistically significant, as well as the interaction between them. After the screening stage, a Box-Behnken design was applied to optimize the cold steam generationconditions. The results of the optimization were evaluated through the Analysis of Variance (ANOVA), graphs of residues versus predicted values and predicted versus observed values, demonstrating that the factors are statistically significant and that the generated model adequately represents the proposed method, obtaining as critical values0.408 and 0.41 mol L-1 of [HCl], 2.80 and 3.86 %(m v-1) of [NaBH4] and 0.27 and 0.19 mL min-1 of CGF for Cd and Hg, respectively. Furthermore, a univariate study to evaluate the influence of L-cysteine and cobalt II concentrations on the cold steam generation process was performed. The proposed method allowed the determination of cadmium and mercury with detection limits (3σ/S) of 0.16 and 0.20 ng L-1, accuracy from the relative standard deviation (RSD) of ERM CA713 of 4.3 and 3.4 % for Cd and Hg, respectively. The accuracy of the method was confirmed by analysis of the residual water reference materials (CA713), oyster tissue (NIST 1566b), spinach leaf (NIST 1570a) and San Joaquin soil (SRM 2709a). A calibration study of the method was carried out to validate that the proposed method does not suffer interference from the sea water matrix. Moreover, the method was satisfactorily applied to three sea water samples collected in the region of Salvador-BA, Brazil. The concentrations of Cd and Hg in the samples are in accordance with those found in the literature and presented values below the maximum limits allowed by the resolution of CONAMA 357/2005 for saline waters class II.